//
// LRUStrategy.h
//
// $Id: LRUStrategy.h 24803 2010-07-23 09:37:57Z anonymous $
//
// Library: Foundation
// Package: Cache
// Module:  LRUStrategy
//
// Definition of the LRUStrategy class.
//
// Copyright (c) 2006, Applied Informatics Software Engineering GmbH.
// and Contributors.
//
// Permission is hereby granted, free of charge, to any person or organization
// obtaining a copy of the software and accompanying documentation covered by
// this license (the "Software") to use, reproduce, display, distribute,
// execute, and transmit the Software, and to prepare derivative works of the
// Software, and to permit third-parties to whom the Software is furnished to
// do so, all subject to the following:
//
// The copyright notices in the Software and this entire statement, including
// the above license grant, this restriction and the following disclaimer,
// must be included in all copies of the Software, in whole or in part, and
// all derivative works of the Software, unless such copies or derivative
// works are solely in the form of machine-executable object code generated by
// a source language processor.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE, TITLE AND NON-INFRINGEMENT. IN NO EVENT
// SHALL THE COPYRIGHT HOLDERS OR ANYONE DISTRIBUTING THE SOFTWARE BE LIABLE
// FOR ANY DAMAGES OR OTHER LIABILITY, WHETHER IN CONTRACT, TORT OR OTHERWISE,
// ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
// DEALINGS IN THE SOFTWARE.
//


#ifndef  Foundation_LRUStrategy_INCLUDED
#define  Foundation_LRUStrategy_INCLUDED


#include "Poco/KeyValueArgs.h"
#include "Poco/ValidArgs.h"
#include "Poco/AbstractStrategy.h"
#include "Poco/EventArgs.h"
#include "Poco/Exception.h"
#include <list>
#include <map>
#include <cstddef>


namespace Poco {


template <class TKey, class TValue>
class LRUStrategy: public AbstractStrategy<TKey, TValue>
  /// An LRUStrategy implements least recently used cache replacement.
{
public:
  typedef std::list<TKey>                   Keys;
  typedef typename Keys::iterator           Iterator;
  typedef typename Keys::const_iterator     ConstIterator;
  typedef std::map<TKey, Iterator>          KeyIndex;
  typedef typename KeyIndex::iterator       IndexIterator;
  typedef typename KeyIndex::const_iterator ConstIndexIterator;

public:
  LRUStrategy(std::size_t size):
    _size(size)
  {
    if (_size < 1) throw InvalidArgumentException("size must be > 0");
  }

  ~LRUStrategy()
  {
  }

  void onAdd(const void*, const KeyValueArgs <TKey, TValue>& args)
  {
    _keys.push_front(args.key());
    std::pair<IndexIterator, bool> stat = _keyIndex.insert(std::make_pair(args.key(), _keys.begin()));
    if (!stat.second)
    {
      stat.first->second = _keys.begin();
    }
  }

  void onRemove(const void*, const TKey& key)
  {
    IndexIterator it = _keyIndex.find(key);

    if (it != _keyIndex.end())
    {
      _keys.erase(it->second);
      _keyIndex.erase(it);
    }
  }

  void onGet(const void*, const TKey& key)
  {
    // LRU: in case of an hit, move to begin
    IndexIterator it = _keyIndex.find(key);

    if (it != _keyIndex.end())
    {
      _keys.splice(_keys.begin(), _keys, it->second); //_keys.erase(it->second)+_keys.push_front(key);
      it->second = _keys.begin();
    }
  }

  void onClear(const void*, const EventArgs& /*args*/)
  {
    _keys.clear();
    _keyIndex.clear();
  }

  void onIsValid(const void*, ValidArgs<TKey>& args)
  {
    if (_keyIndex.find(args.key()) == _keyIndex.end())
    {
      args.invalidate();
    }
  }

  void onReplace(const void*, std::set<TKey>& elemsToRemove)
  {
    // Note: replace only informs the cache which elements
    // it would like to remove!
    // it does not remove them on its own!
    std::size_t curSize = _keyIndex.size();

    if (curSize < _size)
    {
      return;
    }

    std::size_t diff = curSize - _size;
    Iterator it = --_keys.end(); //--keys can never be invoked on an empty list due to the minSize==1 requirement of LRU
    std::size_t i = 0;

    while (i++ < diff)
    {
      elemsToRemove.insert(*it);
      if (it != _keys.begin())
      {
        --it;
      }
    }
  }

protected:
  std::size_t _size;     /// Number of keys the cache can store.
  Keys        _keys;
  KeyIndex    _keyIndex; /// For faster access to _keys
};


} // namespace Poco


#endif
